On Sat, Oct 08, 2016 at 06:24:38PM +0800, Wanpeng Li wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 543b2f2..03a6620 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5472,19 +5472,29 @@ static inline int select_idle_smt(struct task_struct
> *p, struct sched_domain *sd
> */
> static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd,
> int target)
> {
> - struct sched_domain *this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
So select_idle_cpu() <- select_idle_sibling() is called from two places,
both which already hold rcu_read_lock() afaict.
This would've insta-triggered a rcu-lockdep splat otherwise I think.
That is, selsect_task_rq_fair() has rcu_read_lock() taken when calling
this, and task_numa_compare() does too.
> + struct sched_domain *this_sd;
> u64 avg_idle = this_rq()->avg_idle;
> - u64 avg_cost = this_sd->avg_scan_cost;
> + u64 avg_cost;
> u64 time, cost;
> s64 delta;
> int cpu, wrap;
>
> + rcu_read_lock();
> + this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
> + if (!this_sd) {
> + cpu = -1;
> + goto unlock;
> + }
Yes, this is the part that was missing. We need to test this_sd after
the lookup.
Thanks for looking at this!
